1. Field of the Invention
The present invention relates to a joined body of aluminum nitride series ceramics, a method of joining the aluminum nitride series ceramics, and a joining agent which can satisfactorily be used for the joining.
2. Related Art Statement
In conventional semiconductor-producing apparatuses, such as, etching devices and chemical vapor deposition devices, etc., so-called stainless heaters and indirect heating system heaters have been generally used. However, when such heaters are used as heat sources, they are occasionally corroded by an action of halogen-series corrosive gases to form particles and their heat efficiencies are bad. In order to solve such problems, the applicant disclosed formerly in Japanese Patent Application Laid-Open No. 3-26,131 a ceramic heater having a wire of a high melting point embedded in the interior of a dense ceramic substrate, the wire being spirally wound in the substrate of a disc-shape and connected at the both ends to electric terminals. Such a ceramic heater is found to have superior characteristic properties particularly for producing semiconductors.
It has been considered that silicon nitride, aluminum nitride, Sialon and the like nitride series ceramics are preferable ceramics for constituting the substrate of ceramic heaters. Sometimes, a susceptor is mounted on a ceramics heater, and a semiconductive wafer is mounted and heated on the susceptor. The applicant disclosed formerly in Japanese Patent Application Laid-Open No. 5-101,871 that aluminum nitride is preferable as a substrate for such a susceptor and ceramic heaters, because aluminum nitride has an exceedingly high corrosion-resistant property to ClF.sub.3 or the like halogen-series corrosive gases which are frequently used as etching gases and cleaning gases, particularly in semiconductor production apparatuses. In the meantime, because ceramics are hardly processed, studies and researches have been made on joining plural ceramics of a simple shape to each other so as to obtain a part or an element of a complicated shape.
However, generally there is a problem in that at the joining of the interface between the ceramics a third phase is formed having thermal expansion and mechanical properties which are different from those of the ceramics. This third phase is easily fractured by thermal stress due to heating and cooling and various mechanical stresses. Particularly, aluminum nitride series ceramics have low tenacities as compared with silicon nitride ceramics, etc., so that it is largely influenced by the third phase.
Also, when aluminum nitride series ceramics were joined to each other by a glass or a compound consisting mainly of silicon, the third phase remaining at the joining interface is selectively corroded by a plasma of NF.sub.3, ClF.sub.3 or the like halogen series corrosive gas. Such a joined body having the corrodable third phase could not withstand the use in the corrosive environment of semiconductor production apparatuses.
In Japanese Patent Application Laid-Open No. 2-124,778 there is described a method of directly joining substrates made of aluminum nitride sintered bodies to each other wherein the substrates are contacted and heated to 1,800-1,900.degree. C. to an integral body through diffusion joining. However, for joining aluminum nitride sintered bodies to each other by such a diffusion joining method, an extremely high temperature is required. For instance, the temperature of 1,800-1,900.degree. C. is a same extent of high temperature as that required for producing the original aluminum nitride sintered bodies. Thus, the substrates in the joining process are liable to deteriorate and deform, and weak joined bodies of low strength of about 60 MPa or less could only be obtained.
In Japanese Patent Application Laid-Open No. 8-73,280 there is disclosed a joined body of a relatively high strength of aluminum nitride sintered bodies. However, in this method also a high temperature is required for the joining as that required for producing the original aluminum nitride sintered bodies. In addition, the method requires an extremely precise working of the substrates surfaces to a roughness and a flatness of 0.2 .mu.m or less, and such a working of course increases the production cost.